1. Field of the Invention
The present invention relates to the vehicle body structure of an automobile.
2. Description of the Related Art
The structure of a front portion of a vehicle body of an automobile is configured such that front side members which extend in the vehicle-body longitudinal direction are arranged in the vehicle-body widthwise direction at the front portion of the vehicle body. An engine, a transmission and the like are arranged between the respective front side members. By taking a position of a front wheel when a steering wheel is steered at maximum (hereinafter, referred to as “at the time of maximum steering”) into consideration, to avoid the position of the front wheel at the time of maximum steering from interfering with the front side member, a recessed portion is formed in a vehicle-body longitudinally middle portion of the front side member in a state that the recessed portion extends toward a vehicle-body widthwise inner side from a vehicle-body widthwise outer side. Further, with respect to the mode of deformation of the front side member which exhibits the maximum absorption quantity of collision energy of an automobile at the time of collision, a case in which the front side member is axially collapsed from a front end of the front side member to a rear end of the front side member is named.
When the recessed portion is formed in the front side member as in the case of the front side member structure of the related art, a cross-sectional center line of the front end of the front side member and a cross-sectional center line of the recessed portion are displaced from each other in the vehicle-body widthwise direction. Further, to compare a transverse cross-sectional area of the front end of the front side member and a transverse cross-sectional area of the recessed portion of the front side member, the transverse cross-sectional area of the recessed portion of the front side member is set smaller than the transverse cross-sectional area of the front end portion of the front side member. Accordingly, the recessed portion of the front side member forms a fragile portion. With an input which acts along the cross-sectional center line of the front end of the front side member, a bending moment in the vehicle-body widthwise direction is liable to be generated in the vehicle-body longitudinally middle portion of the front side member thus giving rise to the possibility that the recessed portion of the front side member is deformed prior to the deformation of the front end portion of the front side member at the time of collision.
In view of the above, the applicant of the present invention proposed the following vehicle body structure in JP-A-2006-143178. The vehicle body structure is configured such that to rear ends of a pair of front side members which have front end thereof respectively joined to both ends of a front bumper by way of impact absorbing portions, front-side-member upper members and front-side-member lower members which are arranged above and below the respective front side members are connected. Due to such a constitution, collision energy of an automobile at the time of collision is dispersed from the front side members to the front-side-member upper members and the front-side-member lower members arranged above and below the front side members thus absorbing the energy at the time of collision.
Although the vehicle body structure proposed in JP-A-2006-143178 can absorb the energy at the time of collision, the vehicle body structure is still less than optimum with respect to a point which allows the automobile to more efficiently absorb energy at the time of collision or with respect to collapse property. Particularly, with respect to the collapse property of the front-side-member lower member, it is ideal that the member sequentially collapses from a front end side and hence, a joint strength of a rear end side of the front-side-member lower member becomes important. The strength may be imparted to the joint structure by adding a reinforcing bracket or by increasing the number of bolts which constitute fastening members. Such provisions, however, give rise to the increase of the number of parts and the assembling man-hours and, at the same time, give rise to the increase of a weight of the automobile.